Communication systems such as a client server system in which a data sending device and a data receiving device are connected to each other via a network to transmit data from the data sending device to the data receiving device have been widely used.
In Japanese Patent Provisional Publication No. HEI 9-160829 (hereafter, referred to as JP H9-160829A), an example of such a client server system is disclosed. In the client server system disclosed in JP H9-160829A, a client device caches data transmitted from a server. The client device executes a temporary process based on the cached data while checking whether data on the server corresponding to the cached data is updated. If the client device judges that the data on the server corresponding to the cached data is not updated, the client device defines the temporary process as a definitive process and continues to execute a remaining part of the definitive process. If the data on the server corresponding to the cached data is updated on the server, the client device deletes an execution result of the temporary process.
In the case where a data receiving device receives display data from a data sending device and the data receiving device executes a process for displaying information corresponding to the display data, if a waiting time required for receiving the display data from the data sending device is relatively long due to communication speed or a volume of data traffic, a time for displaying information based on the display data on a display of the data receiving device becomes long, thereby causing a user of the client device to become anxious.
The data receiving device may be configured to tentatively display information based on the data cashed in the data receiving device when the data receiving device changes to a data receiving state for receiving display data, as in the case of the client server system disclosed in JP H9-160829A. However, in this case, if the data cached in the data receiving device is older than the corresponding display data on the server (i.e., the data to be displayed is already updated on the server), old information is displayed on the data receiving device tentatively, which confuses a user of the data receiving device.
As an alternative to such a configuration, the data receiving device may be configured to display information representing a waiting state when the data receiving device changes to the data receiving state for receiving display data, so as to notify the user of information indicating that the data receiving device is in the data receiving state. However, in this case, frequency of displaying information indicating that the data receiving device is in the data receiving state may increase, by which the original purpose of displaying information based on the display data transmitted from the data sending device may be deteriorated.